This invention relates to systems and methods for isotope ratio analysis and gas detection, and more particularly to systems and methods for isotope ratio analysis and gas detection using photoacoustics.
In the medical field it has been known to use radioactive isotope labeled compounds to study various conditions. However, the use of radioactive isotopes creates a problem not only from a storage and disposal standpoint, but also from the standpoint that the dosage provided to the patient must be monitored to avoid excessive radiation, illness or other discomfort.
To depart from the drawbacks associated with the use radioactive isotopes, it has been known that a variety of medical conditions can be examined using stable, non-radioactive isotopes. As described in Lee, U.S. Pat. No. 4,684,805, the metabolism of fat can be examined by monitoring the subject's breath after administration of a stable, non-radioactive isotope-labeled fat. Specifically, .sup.13 C-labeled fat can be administered to the subject, the fat being metabolized and the isotope eliminated from the subject as .sup.3 CO.sub.2 during exhalation. The presence and/or concentration of the .sup.13 CO.sub.2 or the ratio of its concentration to naturally occurring .sup.12 CO.sub.2 can be used to analyze the metabolism and its rate under study.
Similarly ileal and liver disfunction can be examined by monitoring exhaled breath following injections of .sup.13 C-labeled bile acid and galactose and examining the exhaled breath for the .sup.13 C isotope present as .sup.13 CO.sub.2. Small intestine bacterial overgrowth can be examined by monitoring exhaled breath for the labeling isotope again occurring as .sup.13 CO.sub.2 following intake of .sup.13 C labeled xylose.
Marshall, U.S. Pat. No. 4,830,010 discloses the use of isotope-labeled urea for diagnosis of gastrointestinal disorders.
As can be appreciated, where applicable, the use of a stable, non-radioactive isotope has vast advantages over the use of a radioactive isotope not only from the storage and disposal standpoint associated with the use of radioactive isotopes but also from a health standpoint.
The shift from use of radioactive isotopes to stable, non-radioactive isotopes in medical analysis only has significant utility if there are satisfactory means and techniques to detect the presence of a labeling isotope. Mass spectrometry is often used for chemical analysis of stable isotopes. A drawback with this technique, however, is that it requires a very high quality vacuum, elaborate sample preparation to remove low levels of water vapor and/or is relatively expensive from an equipment and technician labor standpoint. Furthermore, the mass spectrometric method cannot readily differentiate between compounds with the same mass: for example, .sup.13 CO.sub.2 from .sup.12 COOH and .sup.12 C.sup.16 O.sup.17 O.
Accordingly, if the use of stable, non-radioactive isotopes to study, for example, metabolic rate in a patient are to gain popularity and replace some tests heretofore requiring radioactive isotopes, there is a fundamental need for methods and devices to detect the presence of the labeling, stable, non-radioactive isotope which overcomes the problems associated with the analysis techniques identified above.
In addition to the medical field, isotopic study can also be useful in the geological field. Analysis of the ratio of .sup.13 CO.sub.2 to .sup.12 CO.sub.2 in sedimentation of carbonates or in the atmosphere is important to determine the cycle of CO.sub.2 production and absorption. In Crandall, U.S. Pat. No. 4,517,461 geochemical oil exploration and prospecting by measurement of isotopic compositions of large numbers of individual organic compounds of oil samples is described, to be used to predict locations of other oil reserves or where the oil may have migrated from a common source or formation. In this system there is a need for a detector to detect the presence of the isotope compounds or constituents of interest, which does not suffer from the problems and drawbacks of the analysis techniques such as mass spectroscopy described above.
Still further and as a departure from isotopic analysis, there is a general need for a detector to detect the presence of certain other suspected constituents in a sample. As but several examples, air samples can be monitored and analyzed for toxic vapors such as CO, NH.sub.3, HCl, H.sub.2 S and HF in or about a chemical plant or a power plant or the like. Fast, reliable, and economic detectors directed to the presence of such constituents would constitute a valuable tool to combat pollution and to detect the escape, discharge or presence of harmful compounds. Many current chemical analysis techniques are often unsatisfactory in that they are slow and expensive.
On-Road vehicle emission inspections for pollutants is also important to intercept major pollution offenders and to improve overall air quality. Again, a fast, reliable and accurate method of detection and detector would be a valuable tool to combat air pollution.
As but other examples where a detector and method which is fast, economical and reliable would be important would be in sampling air proximate a natural gas pipeline to determine the presence of leaks. Soil samples which may contain certain dense nonaqueous phase layer chemicals (DNALP) such as chlorobenzene and others as a pollutant are also in need of a detection method, system and detector which is fast, economical and reliable to detect the presence of such pollutants.
As another example, in military or security fields, a fast, reliable and accurate detector and method is needed to determine the presence of explosives or chemical warfare compounds.
The foregoing are but several examples where there is a need for a reliable, inexpensive detector which does not suffer from the drawbacks of mass spectrometry or gas chromatography.